For the industrial manufacture of acrylamide, there are known some relatively new processes whereby acrylamide aqueous solutions are directly obtained from the catalytic hydration reaction of acrylonitrile. Such processes include, for example, a process disclosed by U.S. Pat. No. 3,381,034 employing copper ion; a process disclosed by U.S. Pat. No. 3,631,104 employing copper oxide, copper-chrome oxide, copper-molybdenum oxide or a copper catalyst obtained by reducing them; and a process disclosed by U.S. Pat. No. 3,674,848 employing a copper salt of acid cation resin, etc. In addition to them, there is another process employing such catalysts as Raney copper, Ulmann copper, reduced copper, copper with a carrier etc. (U.S. Pat. Application Ser. No. 56,967, filed July 21, 1970, owned by the assignee of the patent application).
When the acrylamide aqueous solutions prepared in accordance with such processes are further treated through some refining processes, they become acrylamide monomer aqueous solutions of sufficient purity permitting their use, without further process, for paper processing or agglomerating purposes. While it has some advantages for a commercially available products to be in the form of aqueous solution, there are some problems in handling acrylamide aqueous solutions, such as preventing their deterioration in transit or in storage.
This is a new problem and has not been experienced with the conventional sulfuric acid process for the industrial production of acrylamide wherein acrylamide is obtained in a crystallized form by removing by-product ammonium sulfate. The problem still remains unsolved.
The problem in connection with the handling of the acrylamide aqueous solutions that are prepared by catalytic hydration processes arises from the polymerization of acrylamide which is readily polymerized causing deterioration of the products in transit or in storage over a long period of time. As a generally applicable method, it is often adopted in handling readily-polymerizing materials to cause a suitable quantity of a proper polymerization inhibitor to coexist in the solution of such a matter. However, in cases where an acrylamide aqueous solution is polymerized for direct use as an acrylamide prepolymer solution, such concomitant polymerization inhibitor hinders normal polymerization reaction, and then the stable reinforcement of paper or stable agglomeration of effluent treatment cannot be attained as desired.